Method of making a molded waveguide filter with integral tuning posts

ABSTRACT

A method for molding a waveguide filter having integral tuning posts.

United States Patent MacTurk 1 July 29, 1975 [54] METHOD OF MAKING A MOLDED 2,592,614 4/1952 Stoddard 29/600 WAVEGUIDE FILTER WITH INTEGRAL 2,826,524 3/1958 Molloy 204/9 TUNING POSTS 2,870,524 1/1959 Kmnear 204/9 3,261,078 7/1966 Hanemann et a1..... 29/600 [75] Inventor: William L. MacTurk, Claremont, 3,290,762 12/1966 yuzawa 61 /600 Ca]if 3,314,130 4/1967 Sheridan 29/600 3,496,498 2/1970 Kawahashi et al. 333/73 W [73] Assignee: General Dynamics Corporation, 3,696,314 10/1972 Kell et a1 333/73 W Pomona, Calif. 3,713,051 1/1973 Kell 333/73 R [22] Filed FOREIGN PATENTS OR APPLICATIONS 1 1 PP 494,693 798,519 7/1958 United Kingdom 29/600 Related US. Application Data [63] Continuation-impart of Ser. No, 406,058, Oct, 12, Primary ExaminerC. W. Lanham 1973, abandoned. Assistant Examiner-James R. Duzan Attorney, Agent, or FirmA1bert J. Miller; Edward B. [52] US. Cl 29/600; 264/272; 333/73 W J hn n [51] Int. Cl. 11011 11/00 [58] Field of Search 29/600, 601; 333/73 W,

333/83; 264/104, 272; 249/119, 121, 160, [57] ABSTRACT A method for molding a waveguide filter having inte- [56] References Cited gral tuning posts.

UNITED STATES PATENTS 5 Cl 13 D F 1,485,061 2/1924 Ahlgren 249/163 rawmg gums PATENTED JUL29|975 SHEET SHEU PATENTEBJULZTQ ms FIGQEO PATENTEDJULZQIQYS SHEEY Flo METHOD OF MAKING A MOLDED WAVEGUIDE FILTER WITH INTEGRAL TUNING POSTS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of U.S. Pat. application Ser. No. 406,058 filed Oct. 12, 1973, now abandoned.

BACKGROUND OF THE INVENTION Waveguides of various electrical characteristics are widely employed in the reception and transmission of electromagnetic waves. One of the many applications found for such waveguides has been missile systems in which size, weight and reliability are extremely important considerations.

While metal waveguides, such as disclosed in U.S. Pat. Nos. 2,592,614; 3,261,078, and 3,314,130 are suitable for many applications, their weight makes them unsatisfactory for missile applications. Thus, metal coated glass cloth, elastomer, and plastic waveguides such as described in U.S. Pat. Nos. 2,826,524; 3,290,762; and 2,870,524 have been developed.

When, however, it is desirable to utilize a waveguide as a frequency band pass filter, it is necessary that tuning posts be provided in the interior of the hollow waveguide. Conventional waveguide filters are heavy metal devices machined from aluminum, brass, or copper bronze alloys and containing numerous metal tuning posts. The tuning posts are normally made by inserting metal pins into the metal waveguide and soldering the pins in place. Besides being costly to machine, requiring close mechanical tolerances, and not being conducive to manufacture under production conditions, electrical manfunctions were rather common place from excess solder, pin displacement from soldering temperatures and tolerance error buildup.

With other than metal waveguides, no satisfactory method has been found to provide the tuning posts in the interior thereof. In addition to those patents mentioned above, the following patents were cited in U.S. Ser. No. 406,058: U.S. Pat. Nos. 3,713,051; 3,696,314; 1,485,061; 3,496,498; and Great Britain Pat. No. 798,519.

SUMMARY OF THE INVENTION The invention provides a method of molding integral tuning posts having metal tuning screws disposed over them in a waveguide filter. The waveguide filter is molded in two pieces, a waveguide body having integral tuning posts and a waveguide cap, which are then assembled into the waveguide filter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded view of the mold apparatus for the waveguide filter cap;

FIG. 2 is a plan view of the interior face of the mold of the mold apparatus of FIG. 1;

FIG. 3 is a cross-sectional view through the mold cavity of the waveguide filter cap mold apparatus of FIG.

FIG. 4 is a perspective view of a waveguide filter cap produced with the mold apparatus of FIGS. 1-3;

FIG. 5 is an exploded view of the mold apparatus for the waveguide filter body;

FIG. 6 is a perspective view of the mold cover for the waveguide filter body mold apparatus of FIG. 5;

FIG. 7 is a widthwise cross-sectional view of the mold cavity of the waveguide filter body mold apparatus of FIGS. 5 and 6;

FIG. 8 is a lengthwise cross-sectional view of the mold cavity of the waveguide filter body mold apparav tus of FIGS. 5 and 6;

FIG. 9 is a perspective view of a waveguide filter body produced with the mold apparatus of FIGS. 5-8;

FIG. 10 is a perspective view of a waveguide filter assembled from the waveguide filter cap and waveguide filter body and showing the input and output connectors;

FIG. 11 is a perspective view of the waveguide filter of FIG. 10 showing the tuning screws;

FIG. 12 is a lengthwise cross-sectional view of the assembled waveguide filter of FIGS. 10 and 11 taken through the integral tuning posts.

FIG. 13 is a crosswise cross-sectional view of the assembled waveguide filter of FIGS. 10 and 11 taken through an integral tuning post.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The steel mold assembly 10 shown in FIGS. 1-3 is used to form the waveguide filter cap 12 of FIG. 4. The mold assembly 10 basically comprises the mold l4, central plate 16, and cover plate 18.

The mold 14 is generally rectangular in form and includes a plurality of holes partially therethrough extending from the interior surface 20 thereof. As shown in FIG. 2, an input feed post opening 22 and output feed post opening 24 are provided at opposite ends of the interior surface 20. In addition, a number of mounting holes 26 are provided around the periphery of the interior surface 20 of the mold 14.

The central plate 16 includes a like number of mounting holes 28 extending therethrough and individually aligned with the corresponding mounting holes 26 in the mold 14. A rectangular opening 30 in the central plate 16 provides the cavity for the main body or base 40 of waveguide filter cap 12.

A plurality of mounting pins 32, corresponding in number to the number of mounting holes 26 and 28 and aligned therewith, are disposed on the interior surface 34 of the cover plate 18. The pins 32 have a length greater than the thickness of the central plate 16 so as to extend through the mounting holes 28 in the central plate 16 and into the mounting holes 26 in the mold 14. In addition, a plurality of pins 36 project outward from the interior surface 34 of the cover plate 18 into the cavity 30 of the central plate 16. The pins 36 have a length equal to the thickness of the central plate 16. A molding port 38 also extends through the 'cover plate 18 into the cavity 36.

As best shown in FIG. 3, the moldassembly 10 is formed by aligning the mounting holes 26 of the mold 14 and the mounting holes 28 of the central plate 16 with the mounting pins 32 of the cover plate 18. A clamp means (not shown) may be utilized to hold the mold assembly together if desired.

As stated previously, the base 40 of the waveguide filter cap 12 is formed in the cavity 30 in the central plate 16 between the mold 14 and the cover plate 18. The plurality of holes 42 which extend through the base 40 result from the pins 36 in the cavity 30. The input post 44 and output post 46 which extend from the base 40 are formed in the input feed post opening 22 and the output feed post opening 24 respectively, both in the mold 14 and communicating with the cavity 30.

The waveguide filter cap 12 is formed by the injection of molten plastic under pressure into cavity 30 through the port 38 in the cover plate 18. A Lustran ABS plastic at 425F at an injection pressure of 600 psig was injected through a cycle time of 60 seconds, made up of injection and boost for 28 seconds and then a holding time of 32 seconds.

The waveguide filter body 50 shown in FIG. 9 is formed in the steel mold assembly 52 of FIGS. -8. The mold 54 is a generally rectangular structure having a deep central slot or mold cavity 56. The top surface 58 includes a plurality of mounting holes 60 and a molding fill hole 62 communicating with the cavity 56. Additionally each end of the mold 54 includes a plurality of mounting holes.

End plate 68 having mounting pins 70 to engage mold end mounting holes is disposed at one end of the mold 54 while end plate 72 having mounting pins 74 to engage mold end mounting holes is disposed at the opposite end of the mold 54.

An internal mandrel 76 having end mounting holes 78 and 80 is suspended in the cavity 56 of the mold 54 between the end plates 68 and 72. Mounting pin 82 projecting from end plate 68 into mandrel hole 78 and mounting pin 84 projecting from end plate 72 into mandrel hole 80 position the mandrel 76 in the cavity 56.

A plurality of tuning post holes 86 vertically extend through the mandrel 76. Vertically extending positioning holes 88 partially extend downward into the mandrel 76 at either end thereof. Disposed over the mandrel 76 is a thin shim 82. This shim 82 is positioned on the mandrel 76 by means of upwardly extending pins 83 on the mandrel 76 which extend through holes 85 in the shim 81. The shim 81 also includes positioning holes 87 aligned with the positioning holes 88 in the mandrel 76. A cover plate 90 is disposed over the mold 54 and includes mounting pins 92 aligned with the mounting holes 60 on the top surface 58 of the mold 54. Additionally the cover plate 90 includes positioning holes 96 aligned with the positioning holes 87 in the shim 81 and positioning holes 88 of the mandrel 76 and a molding port 98 aligned with the molding fill hole 62 in the top surface 58 of the mold 54. A plurality of pins 94 project from the cover plate 90 into the cavity between the mandrel 76 and the mold 54.

The mold assembly 52 is formed by assemblying the mold 54 and internal mandrel 76 with shim 84 between end plates 68 and 72 and then placing the cover plate 90 on the top thereof. Pins may be inserted through the positioning holes 96 in the cover plate 90, the positioning holes 87 in the shim 81, to the positioning holes 88 in the mandrel 76. Clamp means may also be required.

The mold cavity formed in the mold assembly 52 is an elongated U-shape, there being clearance between both the sides and the bottom of the internal mandrel 76 and the cavity 56 in the mold 54. This forms the U- shaped waveguide filter body 50 while the tuning post holes 86 in the mandrel form the plurality of tuning posts 100. The pins 94 in the cover plate 90 produce holes 102 at the top of each of the walls 104 of the U- shaped waveguide filter body 50. The shim 81 produces tuning posts which are slightly shorter, e.g., 0.015 inches, than the walls 104.

A Lustran ABS plastic was injected into the mold assembly 52 to form the waveguide body and posts in the same molding sequence used to form the waveguide cap 12. The injection pressure is, however, increased from 600 psig to 800 psig.

Following individual molding, the mold assemblies 10 and 52 are disassembled and the waveguide filter cap 12 and waveguide filter body 50 removed. Any plastic flash is then removed from the molded parts.

In order to connect the OSM input and output connectors 106 and 108 to the base of the U-shaped waveguide filter body 54, a plurality of holes are drilled opposite the input and output posts 44 and 46 respectively. Input and output posts 44 and 46 are also drilled to form holes 45 and 47 respectively to accept the OSM connector pins. In addition, the holes 102 in the walls of the body 50 are tapped. A buttressing mandrel (not shown) may be utilized to maintain the required perpendicularity of the waveguide walls 104 during this drilling and tapping of the holes. Additionally, a plurality of holes, equal to the number of tuning posts, are drilled and tapped in the base 40 of the waveguide filter cap 12, one hole being opposite each tuning post 100. Alternately each of these holes described above may be molded into the waveguide filter cap 12 and waveguide filter body 50 by providing additional pins in the mold assemblies 10 and 52, respectively.

After the drilling and tapping of the holes has been completed, the entire waveguide filter body 50 including tuning posts 100 and the entire waveguide filter cap 12 are first copper plated and then gold plated. Prior to the plating, the glossy surface of the molded plastic is removed by a light vapor hone. An electroless copper coating or deposit of approximately 50 X l0 inch is first applied over the waveguide filter body 50 and the cap 12. An approximately 1 mil thick copper plating is then electrodeposited on the waveguide filter body 50 and cap 12 with an 8 amp load current for 40 minutes in a copper tank. A gold flash of X 10 inch is then applied for corrosion purposes.

Once plated, the waveguide filter cap 12 is placed over the waveguide filter body 50 as shown in FIGS. 10 through 13. The plating 101 on the waveguide filter cap 12 and waveguide filter body is illustrated in FIGS. 12 and 13. Screws 114 are used to attach the cap 12 to the body 50. Metal tuning screws 116 are then inserted through holes 112 in the waveguide filter cap 12 into position over the tuning posts 100. The OSM input and output connectors 106 and 108 are screwed into place at the base of the waveguide body 50. This effectively completes the waveguide filter assembly.

Since, as shown in FIGS. 12 and 13, the tuning posts are shorter than the walls 104 of the waveguide filter body 50, there is a gap between the top of the posts 100 and the waveguide filter cap 12. The'metal tuning screws 116 can be positioned to extend varying distances into this gap. This enables tuning of the waveguide filter to provide the proper bandpass and frequency response by inductively or capacitively coupling each tuning post by adjusting each tuning screw. Filters produced by the process of the present invention are lightweight and susceptible to production manufacture. These plastic waveguide filters are less than half as heavy as a comparable metal waveguide filter and are considerably less expensive to produce. They are also much more electrically reliable.

The plastic, including any heat shrinkage, is dimensionally stable to precisely establish the desired filter band pass. The positioning of the tuning post can be made accurate to .0005 inches, which differencewould not be detectable by the electromagnetic field. The center frequency, bandpass, and band width will meet the required engineering specifications. Attentuation versus frequency shows a frequency response within minus 55 db attenuation.

While specific embodiments of the invention have been illustrated and described, it is to be understood that these are provided by way of example only and that the scope of the invention is to be determined by the proper scope of the appended claims.

What I claim is: l. A method of producing a waveguide filter having integral tuning posts comprising the steps of:

molding a substantially U-shaped waveguide filter body having integral tuning posts disposed therein, said integral tuning posts being shorter than the walls of said U-shaped waveguide filter body;

molding a substantially flat waveguide filter cap for the molded waveguide filter body to substantially close the open end of said substantially U-shaped waveguide filter body;

copper plating the waveguide filter body and the waveguide filter cap; gold plating the copper-plated waveguide filter body and the copper-plated waveguide filter cap;

assembling the plated waveguide filter cap and the plated waveguide filter body to form the waveguide filter; and

providing adjustable metal tuning screws in said waveguide filter cap to extend over the integral tuning posts of said waveguide filter body. 2. The method of claim 1 wherein the waveguide filter body and waveguide filter cap are molded of a plastic material.

3. The method of claim 2 wherein said plastic material is Lustran ABS plastic.

4. The method of claim 1 wherein said integral tuning posts are approximately 0.015 inches shorter than the wall of said waveguide filter body.

5. The method of claim 1 wherein the molded waveguide filter cap and body are light vapor honed before copper plating.

6. The method of claim 5 wherein said waveguide filter cap and body are copper plated to a thickness of 1 mil over an electroless copper deposit of 50 X inch.

7. The method of claim 6 wherein said waveguide filter cap and body are gold plated to a thickness of 75 X 10 inch.

8. A method of producing a plastic waveguide filter having integral tuning posts comprising the steps of:

assembling a steel mold having a mold cavity for a waveguide filter cap, said cavity being substantially rectangular in form to produce the waveguide cap base and having openings therein to produce input and output posts extending from the waveguide cap base and pins projecting into the cavity to produce a plurality of holes in the waveguide cap base;

injection molding a plastic waveguide filter cap in the waveguide filter cap assembled steel mold;

disassembling the waveguide filter cap steel mold assembly and removing the molded waveguide filter cap;

assembling a steel mold having a substantially U- shaped mold cavity for a waveguide filter body, said mold including an internal mandrel having openings therein for forming integral tuning posts in the substantially U-shaped body and pins projecting into the mold cavity to produce a plurality of holes at the top of the legs of the U-shaped body, said internal mandrel including a thin shim disposed over the integral tuning post forming openings to shorten the height of the tuning posts to less than the height of the walls of the U-shaped body;

injection molding a plastic waveguide filter body in the waveguide filter body assembled steel mold;

disassembling the waveguide filter body steel mold assembly and removing the molded waveguide filter body;

drilling and tapping holes in the waveguide filter body and waveguide filter cap for the assembly thereof;

copper plating the molded waveguide filter cap and the molded waveguide filter body;

gold plating the copper plated waveguide filter cap and waveguide filter body;

assembling the plated waveguide filter cap to the U- shaped waveguide filter body to form a generally U-shaped waveguide filter with the integral tuning posts extending therebetween, the assembly having a gap between the top of the tuning posts and the waveguide filter cap; and

providing adjustable metal tuning screws in said waveguide filter cap to extend into the gap over the integral tuning posts.

9. The method of claim 8 wherein the gap between the top of the integral tuning posts and the waveguide filter cap is approximately 0.015 inches.

10. The method of claim 8 wherein the molded waveguide filter cap and body are light vapor honed before copper plating.

11. The method of claim 8 wherein said waveguide filter cap and body are copper plated to a thickness of 1 mil over an electroless copper deposit of 50 X 10 inch.

12. The method of claim 11 wherein said waveguide filter cap and body are gold plated to a thickness of X 10 inch.

13. The method of claim 8 wherein input and output connectors are electrically connected to the input and output posts through the base of the U-shaped body.

14. The method of claim 8 wherein said waveguide filter cap steel mold assembly comprises;

a substantially rectangular mold body having input and output post openings and a plurality of mounting holes extending from the interior surface thereof;

a central plate having a rectangular opening therein forming a mold cavity communicating with the input and output post openings in said mold body and having mounting holes aligned with the mounting holes of said mold body; and

a cover plate having mounting pins aligned with and projecting through the central plate mounting holes and into the mold body mounting holes and having a plurality of pins projecting into the mold cavity.

15. The method of claim 8 wherein said waveguide filter body steel mold assembly comprises:

7 8 a substantially rectangular mold body having an elona pair of end plates disposed at either end of said gated Central Slot and a plurality of mOuntiflg holes mold body and internal mandrel and having mount- On the ends and top thereof; ing pins to project into the end mounting openings an internal mandrel disposed in the elongated central slot of said mold body to form a generally U-shaped mold cavity therewith, said mandrel having mountthereof; and a cover plate disposed over the top of the mold body,

ing openings at both ends thereof and a plurality of mandr e1 t end plates and hving mofmting pins tuning post openings therethrough; to PIOJCCt into the top mounting openings of the a flat shim disposed over the tuning post openings of mold ysaid internal mandre; 10 

1. A method of producing a waveguide filter having integral tuning posts comprising the steps of: molding a substantially U-shaped waveguide filter body having integral tuning posts disposed therein, said integral tuning posts being shorter than the walls of said U-shaped waveguide filter body; molding a substantially flat waveguide filter cap for the molded waveguide filter body to substantially close the open end of said substantially U-shaped waveguide filter body; copper plating the waveguide filter body and the waveguide filter cap; gold plating the copper-plated waveguide filter body and the copper-plated waveguide filter cap; assembling the plated waveguide filter cap and the plated waveguide filter body to form the waveguide filter; and providing adjustable metal tuning screws in said waveguide filter cap to extend over the integral tuning posts of said waveguide filter body.
 2. The method of claim 1 wherein the waveguide filter body and waveguide filter cap are molded of a plastic material.
 3. The method of claim 2 wherein said plastic matErial is Lustran ABS plastic.
 4. The method of claim 1 wherein said integral tuning posts are approximately 0.015 inches shorter than the wall of said waveguide filter body.
 5. The method of claim 1 wherein the molded waveguide filter cap and body are light vapor honed before copper plating.
 6. The method of claim 5 wherein said waveguide filter cap and body are copper plated to a thickness of 1 mil over an electroless copper deposit of 50 X 10 6 inch.
 7. The method of claim 6 wherein said waveguide filter cap and body are gold plated to a thickness of 75 X 10 6 inch.
 8. A method of producing a plastic waveguide filter having integral tuning posts comprising the steps of: assembling a steel mold having a mold cavity for a waveguide filter cap, said cavity being substantially rectangular in form to produce the waveguide cap base and having openings therein to produce input and output posts extending from the waveguide cap base and pins projecting into the cavity to produce a plurality of holes in the waveguide cap base; injection molding a plastic waveguide filter cap in the waveguide filter cap assembled steel mold; disassembling the waveguide filter cap steel mold assembly and removing the molded waveguide filter cap; assembling a steel mold having a substantially U-shaped mold cavity for a waveguide filter body, said mold including an internal mandrel having openings therein for forming integral tuning posts in the substantially U-shaped body and pins projecting into the mold cavity to produce a plurality of holes at the top of the legs of the U-shaped body, said internal mandrel including a thin shim disposed over the integral tuning post forming openings to shorten the height of the tuning posts to less than the height of the walls of the U-shaped body; injection molding a plastic waveguide filter body in the waveguide filter body assembled steel mold; disassembling the waveguide filter body steel mold assembly and removing the molded waveguide filter body; drilling and tapping holes in the waveguide filter body and waveguide filter cap for the assembly thereof; copper plating the molded waveguide filter cap and the molded waveguide filter body; gold plating the copper plated waveguide filter cap and waveguide filter body; assembling the plated waveguide filter cap to the U-shaped waveguide filter body to form a generally U-shaped waveguide filter with the integral tuning posts extending therebetween, the assembly having a gap between the top of the tuning posts and the waveguide filter cap; and providing adjustable metal tuning screws in said waveguide filter cap to extend into the gap over the integral tuning posts.
 9. The method of claim 8 wherein the gap between the top of the integral tuning posts and the waveguide filter cap is approximately 0.015 inches.
 10. The method of claim 8 wherein the molded waveguide filter cap and body are light vapor honed before copper plating.
 11. The method of claim 8 wherein said waveguide filter cap and body are copper plated to a thickness of 1 mil over an electroless copper deposit of 50 X 10 6 inch.
 12. The method of claim 11 wherein said waveguide filter cap and body are gold plated to a thickness of 75 X 10 6 inch.
 13. The method of claim 8 wherein input and output connectors are electrically connected to the input and output posts through the base of the U-shaped body.
 14. The method of claim 8 wherein said waveguide filter cap steel mold assembly comprises; a substantially rectangular mold body having input and output post openings and a plurality of mounting holes extending from the interior surface thereof; a central plate having a rectangular opening therein forming a mold cavity communicating with the input and output post openings in said mold body and having mounting holes aligned with the mounting holes of said mold boDy; and a cover plate having mounting pins aligned with and projecting through the central plate mounting holes and into the mold body mounting holes and having a plurality of pins projecting into the mold cavity.
 15. The method of claim 8 wherein said waveguide filter body steel mold assembly comprises: a substantially rectangular mold body having an elongated central slot and a plurality of mounting holes on the ends and top thereof; an internal mandrel disposed in the elongated central slot of said mold body to form a generally U-shaped mold cavity therewith, said mandrel having mounting openings at both ends thereof and a plurality of tuning post openings therethrough; a flat shim disposed over the tuning post openings of said internal mandre; a pair of end plates disposed at either end of said mold body and internal mandrel and having mounting pins to project into the end mounting openings thereof; and a cover plate disposed over the top of the mold body, mandrel, and end plates and having mounting pins to project into the top mounting openings of the mold body. 